The invention relates to a process for preparing acetic acid by the gas-phase oxidation of butenes and of oxygen compounds derived from butene or propene by means of gases containing oxygen or by meas of oxygen, at elevated temperatures and in the presence of vanadate catalysts contaning steam or water vapor. These catalysts are of improved selectivity and can be mounted with or without an inert carrier substance.
The state of the art of acetic acid production and vanadate catalysts useful therein may be ascertained by reference to Kirk-Othmer "Encyclopedia of Chemical Technology," 2nd Edition, Vol. 8 (1966) pp. 386-404 under the section Ethanoic Acid, particularly pages 393-398 wherein synthetic methods are disclosed; Vol. 21 (1970), pp. 171-173 wherein vanadium oxides and vanadates are disclosed; U.S. Pat. Nos. 3,431,297; 3,439,029; 3,459,797 and 3,627,823 of Rudolf Brockhaus; West German Pat. Nos. 1,269,119 and 2,026,744; West German Published Applications No. 2,016,681 (abstracted in Chemical Abstracts at Vol. 76, p. 13835 v) and 2,164,023 the disclosures of which are incorporated herein.
It is known that acetic acid may be prepared by gas-phase oxidation in the presence of catalysts containing mixed oxides of vanadium (vanadates) with, for instance, titanium, tin, antimony, aluminum, silicon, zirconium or molybdenum and tungsten as disclosed in West German patent Nos. 1,269,119 and 2,026,744; West German Published Application 2,164,023; U.S. Pat. Nos. 3,431,297 and 3,459,797. A titanium-vanadium mixed oxide catalyst is a particularly suitable catalyst. The butenes are oxidized in the presence of the cited catalysts in the presence of steam and at elevated temperatures by means of oxygen or of gases containing oxygen.
As disclosed in U.S. Pat. No. 3,431,297 titanium and aluminum vanadate catalysts are produced starting with a solution of vanadium pentoxide and titanium tetrachloride and/or aluminum trichloride in strong hydrochloric acid. Upon neutralization of the hydrogen ions, a mixed oxide is obtained which precipitates. This mixed oxide is designated titanium and/or aluminum vanadate. In the catalysts of U.S. Pat. No. 3,431,297 which are ready to be used, the atomic ratio of titanium and/or aluminum to vanadium is 10:1 to 1:10, preferably 1:05 to 1:2, and therefore include ortho, pyro and meta-vanadates, especially the ortho and pyro-vanadates.
U.S. Pat. No. 3,459,797 discloses the preparation of tin vanadate catalysts for use in the process of converting oxygen and a butene into acetic acid. These tin vanadate catalysts have a molar ratio of tin to vanadium of 10:1 to 1:10, preferably 1:05 to 1:2, and therefore include ortho, pyro and meta vanadates.
According to U.S. Pat. No. 3,439,029 antimony vanadate catalysts are employed in the gas-phase oxidation of butene to acetic acid wherein the atomic ratio of antimony to vanadium is desirably 1:3 to 2:1, preferably 0.9:1 to 1:1.5.
As disclosed in U.S. Pat. No. 3,627,823, oxygen compounds derived from butene or propene, for instance secondary-, tertiary- and isobutanol, isobutyraldehyde, isobutyric acid, acetone and methylethylketone are also used as raw materials for the process of preparing acetic acid wherein the catalysts are vanadates of tin, antimony, titanium and aluminum.
West German Published Application No. 2,016,681 (Rudolf Brockhaus et al, abstracted in Chemical Abstracts, Vol. 76, p. 13835v) discloses that catalysts made from the mixed oxides of vanadium (vanadates) with tin, antimony, titanium and aluminum or made from mixed oxides of vanadium and oxide mixtures of these metals are improved by treating hydroxide precipitates obtained in preparing the metals with an oxidizer, preferably hydrogen peroxide. Though catalysts are obtained in such a manner which allows preparing acetic acid with satisfactory yields and favorable reaction rates. These catalysts nevertheless suffer from several undesirable mechanical properties and hardness especially is unsatisfactory.